Rescue update: DEC RC-25s + / was Re: DEC cartridge ID

joseph lang joe.lang.0000 at
Sat Jun 6 16:39:48 CDT 2015

it's true very little LESI documentation escaped...But the klesi schematic
did. and it's well commented. lots of descriptive signal names. The
hardware to interface to it is almost trivial. I took a couple of hours
looking over the schematic and have written a couple of pages describing
how to make it work. Happy to send to anyone who wants it.
Writing  MSCP emulation is beyond my skill level. But i can read a


On Thu, Jun 4, 2015 at 11:56 PM, Robert Armstrong <bob at> wrote:

> >Ethan Dicks [ethan.dicks at] wrote:
> >did not come with a removable cartridge so I've not been able to spin it
> up
>   Yes, one of the annoyances of the RC25 is that you can't spin it up w/o
> the removable platter in place.  I have only one cartridge myself, and it's
> probably bad.  Somebody needs to come up with a hack to spin up the
> Winchester part alone (hint, hint :-)
> >One I've seen is to nibble a chunk out of the rim of the cover skin (to
> prevent pinching) and run a BC-11-A
> > Unibus ribbon cable out to a BA-11 and stick any number of controllers
> in that
>   Doesn't the 725 have one of the regular bulkhead connector panels on the
> back?  The one with the modular screw in plates?  If so, ISTR that there's
> a cable clamp one that will clear a BC11 cable.
>   In any case, I have no need for such foolishness :-)  I have a perfectly
> good 730 too, with a BA11-K expander in the next rack.  It works great, and
> that configuration (with the 730 instead of the 725) was even supported
> although uncommon.  I should go out in the garage and check how the UNIBUS
> cable is routed for you.
>   Besides, the cool thing (for me, at least) about the 725 was the
> packaging.  Any replacement drive would have to fit inside the original box
> to suit my taste.
>   The best option I've come up with is an SMD UNIBUS controller (I have
> just exactly one!) and a small SMD drive.  There were some small SMD drives
> that I think would fit inside the 725 case.  The front panel wouldn't be
> right, but it's better than nothing.  As you said, SCSI would be better,
> but I don't have a UNIBUS controller.
>   What I'd really like is to build a "LESI disk emulator" that could just
> plug into the AZTEC controller, but as far as I've ever been able to
> determine, DEC never documented LESI.  Or at least none of the
> documentation ever escaped.
>   BTW, my 725 is missing the outer sheet metal skin.  The previous owner
> apparently didn't think it was important and discarded it.  If anybody
> happens to have an extra VAX-11/725 skin, I'd love to know.
> Bob

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